board: ti: am62x: am62x: Include K3 common .env files

Include ti_armv7_common.env and ti/mmc.env, which includes' K3  common
environment variables used across different K3 boards.

This patch depends on
https://lore.kernel.org/all/20230315052745.110502-1-n-francis@ti.com/



Signed-off-by: Nikhil M Jain <n-jain1@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>